1. Field of the Invention
The present invention relates generally to various outer membrane proteins (OMPs) of Moraxella catarrhalis which have been found by the inventors to be useful targets in immunotherapy, such as in the preparation of vaccines or protective antibodies for use in treatment of Moraxella catarrhalis-related diseases. In particular aspects, the present invention concerns antigens identified by molecular weights of 30, 80 and 100 kD, recombinant clones encoding these antigens, antigen fragments derived therefrom, equivalents thereof, as well as to antibodies reactive with these species. Further, the invention concerns methods for the detection of Moraxella catarrhalis antigens and antibodies, as well as the use of specific antigens both in passive and active immunity against Moraxella catarrhalis infections.
2. Description of the Related Art
It was previously thought that Moraxella catarrhalis (previously known as Branhamella catarrhalis or Neisseria catarrhalis) was a harmless saprophyte of the upper respiratory tract. However, during the previous decade, it has been determined that this organism is an important human pathogen. In fact, recent studies have established this Gram-negative diplococcus as the cause of a number of human infections (Murphy, 1989). For example, Moraxella catarrhalis is a leading cause of otitis media, acute maxillary sinusitis as well as generalized infections of the lower respiratory tract (see, e.g., Murphy et al., 1989). Studies have established that the incidence of otitis media and sinusitis attributed to Moraxella catarrhalis infections is increasing, with it being about the third most common causative organism. In fact, reports have identified otitis media as the most common disease for which infants and children receive health care (Consensus, 1989).
The "Consensus" report referred to above concluded that prevention of otitis media is an important health care goal due to both its occurrence in infants and children, as well as certain populations of all age groups. In fact, the total financial burden of otitis media has been estimated to be at least 2.5 billion annually, or approximately 3% of the health care budget. Vaccines were identified as the most desired approach to the prevention of this disease for a number of reasons. For example, it was estimated that if vaccines could reduce the incidence of otitis media by 30%, this outcome could bring about an annual health care savings of at least $400 million. However, while some progress has been made in the development of vaccines for 2 of the 3 common otitis media pathogens, Streptococcus pneumoniae and Haemophilus influenzae, there is no indication that similar progress has been made with respect to Moraxella catarrhalis. This is particularly troublesome in that Moraxella catarrhalis now accounts for approximately 17-20% of all otitis media infection (Murphy, 1989).
Previous attempts have been made to identify and characterize Moraxella catarrhalis antigens that would serve as potentially important targets of the human immune response to infection (Murphy, 1989; Goldblatt et al., 1990; Murphy et al., 1990). Generally speaking, the surface of Moraxella catarrhalis is composed of outer membrane proteins (OMPs), lipooligo-saccharide (LOS) and fimbriae. As Murphy points out, Moraxella catarrhalis appears to be somewhat distinct from other gram-negative bacteria in that attempts to isolate the outer membrane of this organism using detergent fractionation of cell envelopes has generally proven to be unsuccessful in that the procedures did not yield consistent results. Moreover, preparations were found to be contaminated with cytoplasmic membranes which suggest an unusually characteristic of the Moraxella catarrhalis cell envelope.
However, workers in the field have demonstrated the existence of 7 or 8 major OMP species, and these appear to be fairly consistent from Moraxella catarrhalis strain to strain, in spite of the great diversity of stains tested. For example, Campagnari et al. has identified the OMPs by letters A-H beginning with a band of molecular weight 98 Kd (OMP-A) and proceeding to the band with a molecular weight of about 21 Kd (OMP-AH). (Campagnari et al., 1987).
The LOS of Moraxella catarrhalis has also been suggested as a possible target for vaccine development. LOS has been isolated from Moraxella catarrhalis strains and subjected to SDS-PAGE and silver staining (Murphy, 1989). It was reported that all but one strain produced an identical pattern of LOS staining. Thus, it appears that the LOS of Moraxella catarrhalis is very highly antigenically conserved, thus raising the feasibility of using a portion of the LOS molecule as a vaccine component.
Lastly, the Fimbriae have been suggested as a possible vaccine candidate. Fimbriae apparently play a role in adherence and colonization of mucosal services in some bacteria. Workers in the field have postulated that if antigenically conserved epitopes are expressed on fimbriae and can be identified, then it is possible that antibodies to such epitopes might be useful therapeutically, or that such epitopes can serve as vaccine components.
Unfortunately, although various subcomponents of the Moraxella catarrhalis cell have been suggested as places to begin a search for vaccine candidates, there has still been no such candidate identified. Certainly, no antigenic epitope or epitopes have been shown to induce protective antibodies. Thus, it is clear that there is currently a need to identify which, if any, Moraxella catarrhalis component may serve as useful antigens that can, for example, be employed in the preparation of both passive and active immunotherapeutic reagents such as vaccines. Additionally, once such an antigen or antigens is identified, there is a need for providing methods and compositions which will allow the preparation of these vaccines and quantities that will allow their use on a wide scale basis in therapeutic protocols.